A variety of wireless audio systems may be found in the prior art. The following general categories of prior art wireless audio systems are of particular relevance to the present invention, especially as they pertain to creating good quality of service, in the domain of audio information transmission and delivery:                DIGITAL AUDIO—CD audio and techniques for dealing with surface damage on CDs, causing bits to be read incorrectly.        DIGITAL WIRELESS AUDIO—Digital cordless phones are prior art. Digital radios in this application include static channel, FHSS and DSSS.        NETWORK-BASED AUDIO—Audio over Internet techniques (e.g., RealNetworks,® iTunes,™ and various others); Audio over Ethernet; Audio over wireless Ethernet (such as music mover products from Creative, Apple etc.).        ANALOG WIRELESS HI-FI AUDIO—For example, 900 MHz FM (analog) wireless stereo systems (e.g., Recoton,® Sennheiser)        PRO AUDIO—There are specific frequencies available for pro audio (analog FM solutions). These typically overlap with VHF and UHF TV channels, forcing users to determine whether or not there is a conflict in each city. The microphones have 2 FM radio transmitters and the receivers also have 2 radios (and 2 antennas), such that if interference or multipath occurs on one, the audio path continues on the other. Samson, Shure,® and AKG® are examples of companies that sell products in this category.        DIGITAL AUDIO BROADCAST (DAB)—In the UK and increasingly in other countries, the old AM and FM radio is being slowly replaced by DAB stations that transmit high fidelity content over the air in digital form.        SATELLITE RADIO—XM and Sirius are examples of “satellite radio” companies.        DIGITAL AUDIO COMPRESSION—The telephone industry has been using digital audio for decades, and has adopted several simple time-domain compression techniques called μlaw and A-law. These techniques basically apply a table-driven logarithmic representation to the raw data—typically reducing 16-bit samples to 8-bit samples (2 to 1 compression). Digital cordless telephones have applied ADPCM compression to voice audio signals in order to reduce the amount of digital payload.        
Pro Audio (FM analog) solutions achieve high quality of service (QoS) by using two transmit frequencies at the receive side, to ensure continuity of signal transmission if one of the frequencies fails (e.g., if a frequency is interfered with or experiences extreme path loss such as with a multipath null). An objective of the present invention is to provide a wireless audio system capable of achieving levels of QoS and frequency diversity comparable to those achievable with Pro Audio, but using digital, frequency-agile radios; i.e., digital wireless audio (DWA). It is a further objective to provide a wireless audio system that does not require multiple radios at each system node, thus reducing system cost compared to known wireless systems.
One aspect of fidelity in multi-channel audio solution is synchronization between channels. For example, without precise synchronization between left and right channels of a stereo signal, the sound image will be grossly distorted.
Another objective is to provide high QoS using busy ISM bands that do not have licensing requirements (such as the 2.400-2.483 GHz band) while coexisting with other signal traffic in the target radio band. This objective makes it desirable to use relatively low-data-rate, narrow-band radios; i.e., having a narrow footprint in the band, such radios are more likely to be able to find “clean” operating frequencies within the band that will not be interfered with by traffic from other devices. The basic rule here is that the fewer bits of payload that are sent, the less exposed the data is in the air, and thus the greater the QoS.
Achieving desirable performance in audio fidelity in a DWA system entails consideration of generally known principles of digital audio. Fidelity can be measured with such metrics as frequency response/pass band ripple, total harmonic distortion, signal-to-noise ratio, and the like. The challenge comes in implementing the general case in which fidelity and QoS must be maintained at or above desired minimum levels while end-to-end system latency is kept to at or below a desired maximum level. There are other global considerations such as system size, cost, and power consumption that typically have hard constraints in practical embodiments. In view of such constraints, it is commonly necessary to make tradeoffs between fidelity, QoS, and latency. There is accordingly a need for new DWA systems having improved fidelity, QoS, and latency characteristics, but without increasing system size, cost, or power consumption compared with known systems of similar performance. The present invention is directed to the foregoing needs and objectives.